The present invention generally relates to vehicle crash discrimination systems such as used to actuate a vehicle passenger restraint device (e.g. an air bag or seat belt harness), and more particularly to a method of discriminating vehicle crashes having low velocity and long time period characteristics.
A variety of systems for actuating vehicular safety devices are well known in the art. Such systems are used to sense a crash condition and, in response to such a condition, to actuate an air bag, lock a seat belt, or actuate a pretensioner for a seat belt retractor. Typically, the safety device is actuated or deployed into its protective position when an impact exceeding a predetermined magnitude is detected by the actuating system.
One prior art method for crash detection integrates the output of an electronic acceleration sensor over time and compares the result against a time-varying threshold velocity. A major drawback of this method is the wide "grey area" between "fire" and "no-fire" conditions for low-velocity crash conditions (i.e. "soft crashes") often results in an inadvertent deployment of the safety device when deployment is unnecessary, or nondeployment of the safety device when deployment is necessary. If a velocity threshold is established which will prevent a no-fire low-velocity crash pulse from causing actuation of the passenger restraint device, the velocity threshold will also prevent a low-velocity, long-time period crash pulse from causing actuation of the passenger restraint device. This presents an unacceptable and possibly hazardous crash discrimination technique.